
Sea otters carry a favourite rock in a loose pouch of skin under their left forearm and use it as an anvil to crack shellfish, and each otter tends to keep the same stone for years, sometimes for life
Sea otters are the only marine mammal that regularly uses stone tools — and many carry a single favourite rock in a loose skin pouch under the left forearm for years, sometimes for life. A 2024 Science paper explains why the habit matters more than it looks.














